In a typical wireless communication system to transmit data at high data rates, communication is severely impaired as a result of multipath interference. Multipath interference results in such systems when two or more signals are received offset in time. This often occurs in an environment having signal deflecting structures. Each signal deflection delays the arrival of the transmitted signal. These deflections can generate signals having differential path delays exceeding a substantial fraction of the data symbol duration, e.g., where the differential path delay is more than half of the data symbol width, thereby causing overlapping signals that impair or destroy signal intelligibility at the receiver.
Traditionally infrared radiation (IR) communication systems avoided this problem by transmitting data at relatively low data bit rates. By employing low data bit rates, the data symbol duration is much longer than the typical differential path delay due to multipath. Hence, any resultant interference is negligible. Unfortunately, low data bit rate communication is rapidly becoming unacceptable as system designers attempt to meet the demands for high capacity IR communication systems which can efficiently accommodate digitized voice and data. Accordingly, the prior art reflects various methods and devices designed to overcome the effects of multipath interference in a high bit rate IR communication system. One method commonly suggested is channel equalization.
Channel equalization methods typically employ some form of equalization scheme such as, for example, linear equalization, decision feedback equalization (DFE), or maximum-likelihood sequence estimation (MLSE) equalization on the received data in order to correct for the intersymbol interference (ISI) caused by channel-induced distortions such as multipath and Rayleigh fading. As will be appreciated by those skilled in the art, equalization is a very complex and expensive solution to multipath interference, which in many application is impracticable.
Other solutions include point-to-point, multipoint or otherwise aimed communication links. As will be appreciated, however, point-to-point, multipoint or otherwise aimed communication links require either fiber optic cables, direct free-space aimed or reflectively aimed transmission, and therefore typically fail to provide uniform service throughout an area of geographic coverage (cell).
It would therefore be extremely advantageous to provide a wireless IR data communication system which overcomes the problems associated with the prior art.